The present invention relates to electrocardiograph apparatus, and particularly to such apparatus including a system for processing an ECG electrical signal to enable discerning the H-wave in the P-Q interval produced by the HIS-bundle.
ECG's (electrocardiograms) are electrical potential traces, or signal waveforms, accompanied by the contractions of the different cavities of the heart. They are an important aid in the study and diagnosis of abnormal heart activity. A typical ECG signal, produced by placing electrodes against the patient's skin, includes P-, Q-, R-, S- and T-waves which are all easily discernable and thereby aid in diagnosing certain aspects of the heart condition. Another wave, also extremely helpful in diagnosing other aspects of the heart condition, is the H-wave in the P-Q interval produced by the HIS-bundle, it being generally recognized that a prolongation in the H-Q interval is strong evidence of an impending complete heart block. However, the H-wave is so weak, compared to surrounding noise, that it is not discernible in a normal ECG taken by the use of skin electrodes, even when the ECG is amplified by conventional means. Accordingly, in order to discern the H-wave, particularly the H-Q interval, the present procedure is to insert one of the electrodes into the heart itself by means of a catheter. Needless to say, such an invasive procedure is far from satisfactory, since it involves a significant element of danger, is time-consuming, and requires costly equipment. For this reason, H-wave electrocardiography is applied only in a very small number of cases compared to general electrocardiography, thereby depriving many patients of the benefits of this important diagnostic aid.
Several systems have been proposed for the non-invasive discernment of the H-wave in an ECG signal. One proposed technique uses a computer which continuously samples the ECG signal in a ring buffer fashion, and upon interupt, the P-R segment is extracted from the ring buffer and is added to the current average for that segment. This technique, however, requires costly computer equipment and elaborate computer-programming procedures, and is therefore not satisfactory for general practice. Another technique proposed is to record the ECG signal on magnetic tape and then to play the tape in reverse so as to obtain the averages between ORS complexes and P-waves without using a large computer. However, such a system also involves special equipment, procedures, and skills and is therefore also not satisfactory for general practice.
An object of the present invention is to provide electrocardiograph apparatus with a system which is capable of discerning the H-wave and yet which is of low cost and simple operation soas to be suitable for general practice.